Re: Alternator whine on radio

[Jeff W <hjr@buffnet.net>]

What you have is a classic case of EMI (Electromagnetic Interference). 
Unfortunately as you have found, not all cases are easily cleaned up. 
There are two sides to the issue; the item that is causing the
noise,(called emission) and the item that is affected by the noise.
(called susceptability) EMI is always best cleared up by suppression at
the source, in this case the alternator. (or a poorly grounded
alternator or radio)  Alternator noise is generally caused by two
things; the switching of the regulator (usually)or forward bias spikes
caused by a faulty diode in the rectifier bridge.(pretty rare).  Both
are usually effectively suppressed by a capacitor across the B+
(positive) terminal and ground.  Keep in mind, faulty grounds worsen the
problem, and may make it impossible to suppress, especially with "down
the line" in-line inductive supression devices.  In fact, sometimes
these devices can make the noise worse.  In the EMI world, there are two
ways that EMI gets into things, referred to as conducted and radiated. 
(easy way to think about it, conducted gets into the radio on the power
wire, radiated gets into it thru the holes in the chassis)  What you
have is called a conducted emission problem with the alternator, and a
conducted susceptability problem with the radio. These are usually easy
to fix.  Radiated problems are a bitch (high frequency stuff)

I suspect that you may have a ground problem.  I say this because you
also have spark noise.  Is your radio grounded properly?  Keep in mind,
you should have a good, heavy ground wire to a known good ground point,
preferably back to negative battery terminal for best results.  Most
radios/amps come with a long undersized ground wire.  Try clipping the
ground wire short and use a heavy (8 gauge) wire back to the battery and
see if this helps.  However, if the alternator is not grounded properly
in turn, it can superimpose noise on the ground wires.  Check alternator
wiring also.  A ground based problem is easily checked by using an
oscilliscope, difficult without (simply connect to ground at alternator,
and at radio chassis ground & look for both a DC and AC component). 
Look for corrosion, loose connections, etc.   

OEM Alternators rarely cause noise problems anymore.  The reason is
because of a almost universal adoption of PWM (pulse width modulation)
switching schemes, instead of a variable frequency arrangement.  Most
alternator manufacturers now use PWM; I am not sure when Bosch
switched.  Again, keep in mind that if you bought an aftermarket
replacement, who knows what might be used as the regulator technology. 
Check for the noise supression capacitor; if there is one mounted
external (silver can), it may be bad.  Try buying a new one.

Post again if this stuff fails.


Jeff